1. Field of the Invention
The present invention relates to the detection of movement in a picture displayed by a television display.
2. Description of the Related Art
Television receivers have various processing standards including NTSC, IDTV, and EDTV (similar to NTSC). These standards have various picture quality functions including Y/C-separation, interpolation between scanning lines, noise rejection, contour correction, and flare correction. These functions are carried out by using correlation techniques between adjacent display lines in a display frame, as well as correlation techniques between adjacent display frames.
As a picture moves on a television display, a picture movement in space in a vertical direction (with respect to the direction of the display lines) may be quite slow at many portions within the display picture, indicating that the video signals of the adjacent lines are quite similar to each other. A high similarity between the video signals of adjacent lines indicates a high correlation between the adjacent lines. Similarly, if at many portions within the display picture there exists a slow change (movement) in time, the video signals of the adjacent frames will be very similar to each other. This high similarity between the video signals of adjacent frames results in a high correlation between the frames.
A conventional picture processing circuit for improving picture quality which uses the correlations both between the adjacent lines and between the adjacent frames will usually have, for example, a movement detection unit that detects a change of the picture in space in the vertical direction or with respect to time. This movement detection unit may often be used to determine the correlation between adjacent lines and the correlation between adjacent frames.
A conventional movement detection circuit is shown in FIG. 1. The conventional movement detection circuit includes an A/D conversion circuit 150, a movement detecting unit 152, and a color signal movement detecting unit 154.
The color signal movement detecting unit 154 includes a color signal sampling unit 156 for sampling the color signal from the present line of the present frame, a color signal sampling unit 158 for sampling the color signal from the same corresponding line of the preceding frame, a frame delay circuit 160 for providing the video signal with a delay time enough for one frame (in this case, 524 lines), a subtractor 162, a low-pass filter circuit 164 and an absolute value circuit 166.
A video signal is digitized by A/D conversion circuit 150, and a color signal C is separated from the digitized video signal by a comb filter, which is made up of a one-line delay circuit 156a and a subtractor 156b. The color signal C passes through a band pass filter circuit 156c having a center frequency equal to the color subcarrier frequency (fsc), and then an absolute value circuit 156d. The output of the absolute value circuit 156d is supplied to one of the input terminals of the subtractor 162. At the same time, the color signal C is separated from the video signal on a similar line of a preceding frame that has passed through the frame line delay circuit 160 by a comb filter formed of a one-line delay circuit 158a and a subtractor 158b. The color signal then passes through a band pass filter circuit 158c and an absolute value circuit 158d. The output of the absolute value circuit 158d is supplied to another input terminal of subtractor 162. A difference signal .DELTA.C of the color signal between the frames is output from the subtractor 162 to a low-pass filter circuit 164 and an absolute value circuit 166. The absolute value circuit 166 outputs a movement detection signal of the color signal to an input terminal of a maximum value selection circuit 168.
Color signals of corresponding lines of adjacent frames are reversed in phase with respect to each other; thus the subtractor 152a provides a difference signal .DELTA.Y which is indicative of the difference in the luminance signals between frames, and the color signal having an amplitude of 2C. The difference signal .DELTA.Y (including the color signal component) of the luminance signal between frames is output from the subtractor 152a to a low-pass filter circuit 152b for rejecting the high-frequency color signal and an absolute value circuit 152c. The absolute value circuit 152c outputs a movement detection signal of the luminance signal to a second input terminal of the maximum value selecting circuit 168. The maximum value selecting circuit 168 compares the movement detection signal of the color signal with the movement detection signal of the luminance signal and outputs the larger of the two as an ultimate movement detection signal.
The conventional movement detection circuit shown in FIG. 1 suffers from a disadvantage caused by leaking of the color component into the lower-frequency luminance component of the video signal. Since the luminance signal component is generally in a lower frequency range than the color signal component of a video signal, the lower frequency end of the color signal leaks into the movement detection signal of the luminance signal so that a false movement is detected. Also, the rejection characteristic of the low-pass filter circuit 152b is insufficient to fully eliminate the color signal component 2C, so that the color signal appears in the frequency range of the luminance signal. Thus the color signal component cannot be completely rejected. Particularly, the leakage of the color signal tends to occur at the interface portion of magenta and green of the color bar signal, causing picture quality deterioration such as dot interference.
The conventional movement detection circuit shown in FIG. 1 may erroneously detect movement of the color signal when the leakage level of the luminance signal that leaks into the color signal increases. Thus, the conventional movement detection circuit may indicate movement in the color signal, when in fact no such movement has occurred.
This potential for erroneous reading in the ultimate movement detection signal output from the maximum value detecting circuit 168 causes additional problems when a synthesis ratio is generated in response to the ultimate movement detection circuit in order to synthesize Y/C separated color and luminance signals. In practice, the synthesis ratio is usually controlled by detecting only the movement in time of the video signal.
FIG. 2 shows a conventional movement following-type Y/C separation circuit. An A/D converter 170 digitizes the NTSC signal and outputs the digitized signal to a comb filter 172. A line delay circuit 172a and 172b delay the digitized signal by one line. An adding circuit 172c provides an average value (Y-C) of the digitized signal and a digitized signal delayed by two lines output from the line delay circuit 172b. The subtraction circuit 172d subtracts the average value (Y-C) with a line delayed by line delay circuit 172a, hereinafter referred to as the reference line of a first frame. The subtraction circuit 172d divides in half the result of subtraction between the average value (Y-C) and the video signal on the reference line (Y+C) to output a color signal C.sub.1. The color signal C.sub.1 is produced when the video signal undergoes Y/C separation on the basis of correlation between the lines.
The reference frame is delayed one frame by a frame delay circuit 174, which essentially is a 524-line delay circuit, and a line delay circuit 176. The reference line of the delayed frame (e.g., the second frame) is subtracted from the reference line of the first frame by a subtracting circuit 178. The subtracting circuit 178 divides the subtraction result by two and outputs a color signal C.sub.1 which has undergone Y/C separation on the basis of the correlation between the first frame and the second frame.
The color signal C.sub.1 which was Y/C separated based upon correlation between the lines and the color signal C, which was Y/C separated based upon correlation between the frames are both input into a color movement following synthesis circuit 180. The ultimate movement detection signal from FIG. 1 is input to the color movement following synthesis circuit 180 to dynamically vary a synthesis ratio. The color movement following synthesis circuit synthesizes a synthesized color signal from the color signals C.sub.1 and C.sub.1 in accordance with the synthesis ratio and outputs the synthesized color signal to output terminal OC.
The corresponding Y/C separated luminance signal, hereinafter the corrected luminance signal, is generated by a subtractor 182 by subtracting the synthesized color signal from the video signal in the reference line (Y+C) of the first frame. The subtractor 182 divides the subtraction result by two and outputs the corrected luminance signal to output terminal OY.
In addition to the disadvantages of relying on an inaccurate ultimate movement detection signal, the Y/C separation circuit of FIG. 2 uses the frame delay circuit 174 separate from the frame delay circuit 160 of the movement detection circuit in FIG. 1. As a result, the use of two separate memory delay circuits causes increased complexity and costs. Thus, in order to implement the prior art devices in hardware, it would be necessary to provide: the A/D converter 150, the comb filters 156 and 158, and the frame delay 160 on a first IC chip; the remainder of the movement detection circuit on a second IC chip; the A/D converter 170, the comb filter 172 and the frame delay 174 on a third IC chip; and the remainder of the Y/C separation circuit on a fourth IC chip.
Therefore, the hardware implementation of the prior art devices suffers substantial problems with printed circuit boards and mounting space, thus increasing costs and causing added reliability problems.